Multi-Device Networking Application MCP23017E/SS I2C Cascading Technology Analysis

^{September 16, 2025 News — With the rapid development of Industry 4.0 and IoT technology, the demand for device I/O expansion capabilities is increasingly growing. The MCP23017-E/SS 16-bit I/O expander chip launched by Shenzhen Anxinruo Technology Co., Ltd., with its powerful interface expansion capabilities and flexible configuration options, is becoming an important choice for industrial control, smart home, and IoT devices.}

^{The MCP23017-E/SS utilizes an I²C interface to achieve 16-bit I/O expansion, supporting up to 8 device cascades through 3 address pins, and offers 400kHz high-speed communication with configurable interrupt output. The chip features 16 independently programmable GPIOs, supporting input/output direction setting, internal pull-up resistors, and polarity inversion. With an operating voltage range of 2.7V-5.5V, each I/O port can provide 25mA drive current, and power consumption in standby mode is below 1μA. Housed in an SSOP-28 industrial-grade package, it provides a comprehensive interface expansion solution for embedded systems.} 

^{Core Functional Modules}                                                                          

^{1.Communication Interface Module}

^{I²C serial interface}

^{SCL: Serial clock input pin}

^{SDA: Bidirectional serial data line}

^{Supports standard mode (100kHz) and fast mode (400kHz)}

^{2.Address Decoding Module: 3-bit hardware address supports 8-device cascading
3.Interrupt Control Module: Provides dual interrupt outputs (INTA/INTB)
4.Data Conversion Module: Implements serial-to-parallel data conversion
5.GPIO Module: 16-bit programmable I/O ports
6.Register Bank: Stores configuration parameters and control status}

Workflow
 

1.Initialization Configuration

Configure control registers via I²C interface

Set I/O direction, pull-up resistors, and other parameters

2.Data Communication

Host sends control commands and data via I²C

Serializer converts serial data to parallel data

Configuration registers update corresponding settings

3.Interrupt Handling

GPIO state changes trigger interrupt logic

INTA/INTB pins send interrupt signals to the host

Host reads interrupt flag register to determine the interrupt source

^{Feature Advantages:}

^{High Integration: 16-bit I/O expansion implemented in a single chip}

^{Flexible Configuration: Each I/O port can be independently programmed}

^{Low Power Consumption: Standby current < 1μA}

^{Strong Drive Capability: 25mA drive current per port}

1. Byte Write Operation

^{Timing Description:}

^{Start Condition (S): Master generates start signal}

^{Device Opcode (OP): 7-bit device address (0100AAA) + write flag bit (0)}

^{Register Address (ADDR): Specifies target register for writing}

^{Data Input (DIN): Data to be written to the register}

^{Stop Condition (P): Master generates stop signal}

2. Sequential Write Operation

Timing Description:

Start Condition (S): Host generates start signal

Device Opcode (OP): 7-bit device address + write flag bit

Register Address (ADDR): Specifies starting register address

Data Input (DIN): Continuously writes multiple data with auto-incrementing address

Stop Condition (P): Host generates stop signal

3. Key Signal Definitions

^{4. Timing Characteristics Parameters}

^{Communication Rate: Supports 100kHz (standard mode) and 400kHz (fast mode)}

^{Data Validity: SDA data must remain stable during SCL high level}

^{Start Condition: SDA transitions from high to low while SCL is high}

^{Stop Condition: SDA transitions from low to high while SCL is high}

^{5. Application Notes}

^{Device Address: 0100AAA, where AAA is determined by A2/A1/A0 pins}

^{Data Transmission: MSB first, 8-bit data + 1-bit ACK}

^{Acknowledge Signal: Receiver generates ACK signal after each byte}

^{Timing Requirements: Must meet I²C specification parameters (t_SU, t_HD, etc.)}

^{This timing diagram illustrates the complete I²C communication protocol of the MCP23017-E/SO, providing accurate timing references for device programming and system integration.}

GPIO Port Pins

^{1.Power Pins}

^{VDD (Pin 9): Positive power supply input (2.7V to 5.5V)}

^{VSS (Pin 10): Power ground}

^{2.Control and Configuration Pins}

^{RESET (Pin 18): Reset input (active low)}

^{INTA (Pin 19): PORT A interrupt output}

^{INTB (Pin 20): PORT B interrupt output}

^{3.Address Configuration Pins}

^{A0 (Pin 15): I2C address selection bit 0}

^{A1 (Pin 16): I2C address selection bit 1}

^{A2 (Pin 17): I2C address selection bit 2}

^{4.Special Pins}

^{NC (Pins 11, 14): No connection}

^{Thermal Pad (Bottom): Heat dissipation pad, must be grounded}

^{5.Package Characteristics}

^{Package Type: SOIC-28}

^{Pin Pitch: 1.27mm}

^{Operating Temperature: -40°C to +85°C}

^{Thermal Design: Bottom thermal pad must be connected to PCB ground plane}

^{This pin configuration adopts the standard SOIC-28 package, providing a reliable I/O expansion solution for industrial control and embedded systems. All GPIO pins support independent configuration and 25mA drive capability.}

^{Protocol Operation Modes}

^{1. Single-Byte Write Operation}

^{2. Multi-Byte Sequential Write Operation}

^{3. Single-Byte Read Operation}

^{4. Multi-Byte Sequential Read Operation}

^{5. Mixed Operation Mode}

^{Key Protocol Features}

^{Address Pointer Management}

^{Address pointer automatically updates during write operations}

^{Pointer auto-increments during sequential read/write operations}

^{Supports continuous access across register boundaries}

^{Data Validity}

^{Data remains stable during SCL high level}

^{Each byte requires an acknowledgment (ACK/NACK)}

^{MSB-first transmission}

^{Error Handling Mechanism}

^{Slave non-acknowledgment (NACK) detection}

^{Bus timeout protection}

^{Clock stretching support}

^{Timing Requirements}

^{This protocol is fully compatible with the standard I²C specification, providing flexible data transmission methods that support both single-byte and burst transfer modes. It enables efficient configuration and control of all functional registers in the MCP23017.}